docs: def handle_nested_relation(self, line: str, position: int, tokens: ParseResults):
          """Handle nested statements.
  
          If :code:`allow_nested` is False, raises a ``NestedRelationWarning``.
  
          :raises: NestedRelationWarning
          """
          if not self.allow_nested:
              raise NestedRelationWarning(self.get_line_number(), line, position)
  
          self._handle_relation_harness(line, position, {
              SUBJECT: tokens[SUBJECT],
              RELATION: tokens[RELATION],
              OBJECT: tokens[OBJECT][SUBJECT],
          })
  
          self._handle_relation_harness(line, position, {
              SUBJECT: tokens[OBJECT][SUBJECT],
              RELATION: tokens[OBJECT][RELATION],
              OBJECT: tokens[OBJECT][OBJECT],
          })
          return tokens